The invention relates generally to barrier coatings. More specifically, the invention relates to barrier coatings that are used in optoelectronic devices.
Optical and optoelectronic devices that are susceptible to reactive chemical species normally encountered in the environment, require barrier coatings with desirable light transmission properties.
Multilayer barrier coatings desirably are effective barriers against reactive species like oxygen and water vapor. To achieve desired barrier properties it is known in the art to try find layers of materials of various organic and inorganic compositions. Such materials commonly have different indices of refraction, normally resulting in degradation in optical transmission through the barrier layer. Prior approaches have focused on engineering the thickness of the layers to take advantage of multiple-interference to improve light transmission efficiency. However, one has to retain certain thickness of the layers in order to maintain the performance of the barrier, and thus it is not always easy to engineer the thickness. Furthermore, in a mass production environment it is difficult to achieve exact thickness control of the layers. Also, it has been suggested that in multilayer barriers, the interface between layers of different materials is generally weak due to incompatibility of adjacent materials and the layers, thus, are prone to be delaminated.
Organic-inorganic coating compositions desirably may be used to minimize moisture and oxygen permeation rates through the barrier coating. It has been speculated that the organic zone sandwiched between two inorganic zones decouples the defects in one inorganic zone to another. Thick organic zones in the coating are effective in decoupling the defects. However, inorganic materials typically have a refractive index n about 1.8 and organic materials typically have a refractive index n about 1.5. Due to the refractive index mismatch, large amplitude interference fringes are observed with thick organic zones in the coating. Desired optical performance achieved by maintaining organic zone thickness as thin as possible, degrades the barrier properties of the coating.
Therefore, there is need for barrier coatings that are not only robust, having low diffusion rates for environmentally reactive species, but also have desirable optical properties and can easily be mass produced.